Figure 3

Transmission electron micrographs (TEM) of the cell surface of Bihospites bacati n. gen. et sp. A. Cross-section of cell showing a series of S-shaped folds in the cell surface. Elongated extrusomes (E) positioned beneath the raised articulation zones between the S-shaped folds (S). Cell surface covered with rod-shaped bacteria (black arrowheads), in cross section, and spherical-shaped bacteria (white arrowheads). Mitochondrion-derived organelles (MtD) underlie the cell surface. (bar = 1 μm). B. TEM showing mitochondrion-derived organelles (MtD) with zero to two cristae (arrow). Arrowheads show transverse profiles of rod-shaped episymbionts on cell surface. C. High magnification TEM of the host cell surface showing glycogalyx (GL) connecting episymbionts to plasma membrane. Plasma membrane subtended by a thick layer of glycoprotein (double arrowhead) and a continuous row of microtubules linked by short 'arms' (arrowhead). Mitochondrion-derived organelles (MtD) positioned between the row of microtubules and the endoplasmic reticulum (ER). D. Oblique TEM section of spherical-shaped episymbiont showing electron-dense apical operculum (black arrow) and the extrusive thread coiled around a densely stained core region (white arrow). E. High magnification TEM of cell surface showing mitochondrion-derived organelles (MtD), rod-shaped episymbionts (arrowheads), and spherical-shaped episymbiont (black arrow) sitting within a corresponding concavity in the host cell. Core region of the spherical-shaped episymbiont (white arrow) in longitudinal section. F. TEM of spherical-shaped episymbiont showing discharged extrusive thread (arrow). Electron-dense material corresponding to the core is positioned at the tip of the discharged thread (arrow). Arrowheads indicate rod-shaped bacteria on cell surface (B-F bar = 500 nm).